<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>111</title>
		<style type="text/css">
			.box1{
				width: 12.5rem;
				height: 12.5rem;
				background-color: #bfa;
			}
			.box1::before{
				content:"";
				display: table;
			}
			.box2{
				width:100px;
				height: 100px;
				background-color: orange;
				margin-top: 100px;
			}
			/* clearfix可以直接解决高度塌陷和外边距的问题 */
			.clearfix::before,
			.clearfix::after{
				content:"";
				display:table;
				clear:both;
			}
		</style>
	</head>
	<body>
		<div class="box1 clearfix">
			<div class="box2"></div>			
		</div>
	</body>
</html>
